LONDON 
In a drive to inoculate people against swine flu before winter, many European governments say they will fast-track the testing of a vaccine, arousing concern among some experts about safety and proper doses.

The European Medicines Agency, the EU's top drug regulatory body, is accelerating the approval process for swine flu vaccine, and countries such as Britain, Greece, France and Sweden say they'll start using the vaccine after it's greenlighted – possibly within weeks.

In an interview with The Associated Press, Dr. Keiji Fukuda, the World Health Organization's flu chief, warned about the potential dangers of untested vaccines, although he stopped short of criticizing Europe's approach outright.

"One of the things which cannot be compromised is the safety of vaccines," he said Friday. "There are certain areas where you can make economies, perhaps, but certain areas where you simply do not try to make any economies."

Flu vaccines have been used for 40 years, and many experts say extensive testing is unnecessary, since the swine flu vaccine will simply contain a new ingredient: the swine flu virus.

But European officials won't know if the new vaccine causes any rare side effects until millions of people get the shots. Still, they say the benefit of saving lives is worth the gamble.

"Everybody is doing the best they can in a situation which is far from ideal," said Martin Harvey-Allchurch, a spokesman for the European Medicines Agency. "With the winter flu season approaching, we need to make sure the vaccine is available."

In Europe, flu vaccines are usually tested on hundreds of people for several weeks or months, to ensure the immune system produces enough antibodies to fight the infection.

But to ensure swine flu vaccine is available as soon as possible, the European Medicines Agency is allowing companies to skip testing in large numbers of people before the vaccine is approved.

The main issue is probably that without thorough testing it's difficult to gauge the effective dosage – meaning Europeans might get too weak a vaccine. It's unlikely the vaccine would endanger anyone, but until it is used in large numbers of people, no one will know for sure.

Europeans appear ready to use the vaccine widely before conducting any big studies to prove it is safe and effective. Neither the vaccine makers nor the European Medicines Agency would specify what basic safety tests are being done.

The U.S. is taking a more cautious approach: the government called Wednesday for several thousand volunteers to be injected with the swine flu vaccine in tests beginning in August to assess the vaccine's safety. American officials said results should be ready by the time the U.S. plans to roll out a vaccination campaign in October.

Results from the U.S. tests will be of limited use to Europe, since countries like Britain plan to start vaccinating as early as August – before any American trial data is available. The vaccines used in the U.S. will also be different from those in Europe.